Date: Mon, 21 Aug 2006 22:11:45 -0700
From: Andrew Morton <akpm@osdl.org>
To: Nathan Lynch <ntl@pobox.com>
Cc: Paul Jackson <pj@sgi.com>, Anton Blanchard <anton@samba.org>,
       simon.derr@bull.net, nathanl@austin.ibm.com,
       linux-kernel@vger.kernel.org
Subject: Re: cpusets not cpu hotplug aware
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On Tue, 22 Aug 2006 00:04:01 -0500
Nathan Lynch <ntl@pobox.com> wrote:

> > If the kernel provider (ie: distro) has enabled cpusets then it would be
> > appropriate that they also provide a hotplug script which detects whether their
> > user is actually using cpusets and if not, to take some sensible default action. 
> > ie: add the newly-added CPU to the system's single cpuset, no?
> 
> I think it would be more sensible for the default (i.e. user hasn't
> explicitly configured any cpusets) behavior on a CONFIG_CPUSETS=y
> kernel to match the behavior with a CONFIG_CPUSETS=n kernel.

Well...  why?  If he-who-configured the kernel chose cpusets then it's
reasonable to expect he-who-configures to have appropriate userspace
support for that kernel.

>  Right
> now we don't have that.  Binding a task to a newly added cpu just
> fails if CONFIG_CPUSETS=y, but it works if CONFIG_CPUSETS=n.

Sure.  That's because we're not taking appropriate (ie any) action when a
CPU is added.
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